The Daily Omnivore

Fisherian runaway is a model of sexual selection, first proposed by R.A. Fisher in 1915, and expanded upon in his 1930 book ‘The Genetical Theory of Natural Selection,’ that suggests an explanation for sexual selection of traits that do not obviously increase fitness of survival, based upon a positive feedback ‘runaway’ mechanism. Fisher’s explanation is that selection of such traits is a result of sexual preference; that members of the opposite sex find a trait desirable. This preference makes the trait advantageous, which in a circular fashion makes having a preference for the trait advantageous.

The process is termed ‘runaway’ because over time, it would facilitate the development of greater preference and more pronounced traits, until the costs of producing the trait balance the reproductive benefit of possessing it. By way of example, the peacock’s tail requires a great deal of energy to grow and maintain, it reduces the bird’s agility, and it may increase the animal’s visibility to predators. Yet it has evolved, indicating that birds with longer tails have some advantage.

read more »

The Red Queen is the name of an evolutionary theory of Leigh Van Valen and, later, a book by Matt Ridley. The term is taken from the Red Queen’s race in Lewis Carroll’s ‘Through the Looking-Glass.’ The Red Queen said, ‘It takes all the running you can do, to keep in the same place.’ The Red Queen principle can be stated as follows: ‘For an evolutionary system, continuing development is needed just to maintain its fitness relative to the systems it is co-evolving with.’

The hypothesis is used to explain two different phenomena: the advantage of sexual reproduction at the level of individuals, and the constant evolutionary arms race between competing species. Ridley’s book takes Van Valen’s idea, which is about co-evolution, and extends it into a discussion about sexual selection in humans. It argues that few aspects of human nature can be understood apart from sex, since human nature is a product of evolution, and evolution in our case is driven by sexual selection. Its counterpart is the Court Jester Hypothesis, which proposes that evolution is driven mostly by abiotic environmental events and forces like climate.

read more »

Concealed ovulation or hidden estrus is the lack of distinctive signaling that the adult female of a species is ‘in heat’ and near ovulation. These signals may include swelling and redness of the genitalia in baboons and bonobos, pheromone release in the feline family, etc. By comparison, the females of humans and a few other species have few external signs of fecundity, making it difficult to tell, by means of external signs only, whether or not a female is near ovulation.

Several hypotheses regarding human evolution integrate the idea that human females increasingly required supplemental paternal investment in their offspring. This suggests human females concealed ovulation to obtain male aid in rearing offspring. If human females no longer signaled the time of ovulation, males would be unable to detect the exact period in which they were fecund. This led to a change in their mating strategy; rather than seeking multiple female partners and mating with them hoping they were fecund during that period, males instead chose to mate with a particular female multiple times throughout her menstrual cycle. A mating would be successful in resulting in conception when it occurred during ovulation, and thus, frequent matings, necessitated by the effects of concealed ovulation, would be most successful.

read more »